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Pedicle screw system for osteosynthesis

  • US 5,782,833 A
  • Filed: 12/20/1996
  • Issued: 07/21/1998
  • Est. Priority Date: 12/20/1996
  • Status: Expired due to Term
First Claim
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1. A pedicle screw assembly for use in conjunction with a rod for immobilizing bone segments comprising:

  • a screw having a cylindrical threaded shaft and a head, the head having a larger diameter than the shaft with a generally spherically convex bottom section jointed to the shaft and a top section defining a wrench engaging surface so that the screw may be rotatably inserted into a bone segment;

    a polyaxial housing having a top, middle and bottom section, with a stepped axial bore therethrough, the diameter of the bore in the bottom section being larger than the diameter of the cylindrical shaft and smaller than the diameter of the screw head, the diameter of the bore in the top section of the housing having a diameter greater than the diameter of the head of the screw, the middle section of the housing having a generally spherically concave inside surface extending between the bore diameters in the top and bottom sections whereby the cylindrical shaft of the screw may pass through the housing while the head is retained in the middle section of the housing, the top section of the housing defining a pair of spaced upstanding posts with a threaded inside surface, the posts defining a slot therebetween for receiving the rod;

    a cup-shaped cap adapted to be inserted over the top section of the housing after the rod has been inserted through the housing slot, the cap having a bottom defining a pair of spaced openings for receiving the posts and a cross-connector spanning the lateral width of the inside surface of the cap between the openings, the cross-connector having a lower concave surface for engaging the rod and an upper surface;

    a set screw having a head with a wrench engaging surface, a threaded shaft adapted to be threadably received in the threaded surface of the housing and a free end for engaging the upper surface of the cross-connector of the cap to secure the rod between the cross-connector and the screw head; and

    a washer with a top and bottom, the bottom of the washer including a concave surface adapted to engage the head of the screw, the top of the washer having a concave recess adapted to engage the rod, the washer being located within the polyaxial housing between the head of the screw and the rod.

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